Technical Field
The present disclosure relates to an ester wax, a toner, a developer, a toner storing unit, and an image forming apparatus.
Description of the Related Art
An electrophotographic image forming apparatus is generally equipped with a fixing device that fixes a toner image on a medium (e.g., paper sheet) by heat.
Lately, in place of conventional oil fixing devices that have a silicone oil coating for preventing toner from fixedly adhering thereto, oilless fixing devices are widely used in combination with wax-containing toners. The wax in the toner is melted when the toner is fixed on a medium, thus preventing the toner from adhering to the surface of the fixing device. Oilless fixing devices are much simpler than oil fixing devices in configuration and free from a silicone oil contamination problem.
As the wax in the toner, hydrocarbon waxes (e.g., polyethylene wax, paraffin wax), aliphatic alcohols, synthetic polyester waxes, natural waxes composed primarily of ester waxes (e.g., carnauba wax), and mixtures thereof, have been used.
Environmental issues are attracting high interest all over the world. There are various accreditation criteria for volatile organic compounds (VOC), ozone, dust, fine particles, and ultrafine particles particularly generated in electrophotographic image forming processes performed by copiers, multifunction peripherals, or printers. For example, the Blue Angel Mark is known as a German ecolabel for products and services that have environmentally friendly aspects.
Any product without the Blue Angel Mark certification is available for sale, but such a product is likely considered to be environmentally unfriendly, especially by government offices. Thus, the Blue Angle Mark certification has a significant influence on product sales.
Certification criteria for the Blue Angel Mark include the dust criterion. According to the dust criterion, the amount of dust is required to be less than 4 mg/h. Here, the amount of dust is determined by operating an image forming apparatus in a sealed chamber, sucking the air from the chamber through a quartz filter, and measuring the increased mass of the quartz filter. Dust generated from the image forming apparatus generally contains a wax included in toner. In a case in which the toner includes a paraffin wax that expresses a relatively high saturated vapor pressure even at a temperature lower than the boiling point, disadvantageously, the paraffin wax will vaporize when the toner is fixed on a medium and adhere to the quartz filter.
By contrast, in a case in which the toner includes an ester wax that expresses an extremely low vapor pressure at a fixing temperature, the amount of generated dust will be very little, which is preferable. In view of this situation, toners containing an ester wax only, as well as toners containing both an ester wax and a paraffin wax, have been proposed.
The fine particle and ultrafine particle criterion have been added to the Blue Angel Mark.
The Blue Angel Mark (RAL-UZ 171, revised in January 2013) defines fine particles and ultrafine particles as particles measurable by a particle size measuring instrument having a measurable particle diameter range of from 7 to 300 nm.
The Blue Angel Mark criterion requires that the number of fine particles and ultrafine particles generated during a 10-minute operation of an image forming apparatus be less than 3.5×1011/10 min. The Blue Angel Mark criterion concerns neither the substance nor the total mass of fine particle and ultrafine particles, and does concern only the number of fine particles and ultrafine particles measured by the particle size measuring instrument. The rate of generation of fine particles and ultrafine particles has no relation to the image forming speed of the image forming apparatus. According to the Blue Angel Mark, the rate of generation of fine particles and ultrafine particles is determined from the amount of fine particles and ultrafine particles generated while the image forming apparatus is in continuous operation for 10 minutes.
A widely-used particle size measuring instrument Fast Mobility Particle Sizer (FMPS) can measure particles having a particle diameter of from 5.6 to 560 nm. Thus, particles which are measurable by the FMPS are included in the fine particles and ultrafine particles defined by the Blue Angel Mark. In the present disclosure, among fine particles and ultrafine particles generated during a 10-minute operation of an image forming apparatus, particles having a particle diameter of from 5.6 to 560 nm when measured by FMPS are defined as UFP.
UFP may be generated from various parts in the image forming apparatus. In particular, it has already been confirmed that the fixing device is the main cause of generation of UFP, based on an experimental result that the UFP concentration is drastically increased when only the fixing device is put into operation. As an example, it has been confirmed that UFP may include siloxane generated from a rubber layer included in a fixing member (e.g., roller, belt).
As another example, it has been confirmed that UFP may include substances included in toner. This is based on the fact that the amount of UFP generated during formation of an image used for a certification criteria test of the Blue Angel Mark becomes nearly 1.5 to 5 times that during formation of a blank white image. This indicates that UFP generated during the image formation contains substances generated from toner. Thus, to suppress generation of UFP from an image forming apparatus, generation of UFP from toner should be suppressed.
It has already been reported that there is a case in which a paraffin wax included in toner becomes UFP.